The present invention relates to a repetition pipette.
German patent 29 26 691 discloses a repetition pipette in which the syringe receiving section is a U-shaped groove in a pipette housing into which a syringe flange can be inserted. In the receiving section the syringe flange is biased by a compression spring towards the delivery opening. The syringe piston includes a cylindrical actuating portion adapted to be fixed in the receiving member by clamping means. The piston returning means comprises a lever which extends from the receiving member through a lateral housing slot. The piston can be withdrawn from the syringe by moving the lever away from the syringe receiving portion. The actuating element of the piston advancing means is an actuating lever which is pivotally mounted on the side of the rack which does not include any toothing. The actuating lever includes the pawl and an actuating end extending from the housing on the toothing side of the rack. The withholding element of the step width adjusting means is a tongue which covers the toothing of the rack more or less depending on the settings of a rotary knob. The tongue prevents a pawl from engaging the rack upon actuation of the lever when the tongue is in the covering range. In the other range the pawl engages the toothing so as to drive the latter and the piston connected thereto for one advancing step. As a result the width of the advancing step and the volume dispensed by the syringe are adjustable by the rotary knob.
The stroke of the actuating lever includes an idle stroke portion for preventing the pawl from engagement with the toothing by the tongue, and a work stroke portion for having the pawl engage the toothing. The idle stroke portion is the greater and the work stroke portion the smaller, the smaller the adjusted step width and the smaller the liquid volume are. The user has to pivot the actuating lever through the idle stroke portion (which is substantial for many settings) even so this does not displace the piston within the syringe.
The problem to be solved by the invention is to provide a repetition pipette the handling of which is simplified.